Method for covering damaged protective layer areas, device for implementing said method and transport system

ABSTRACT

The invention relates first of all to a method for covering areas of damaged protective coating on containers or the like, in which, according to the invention, protective coating material is stamped on to the zone in which the damaged areas occur. The invention also describes an apparatus for carrying out the method in which a carrier unit is provided for stamping protective coating material on to the damaged area. Apparatus is provided for positioning the carrier unit with respect to the container.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to methods and apparatus for manufacturingmetal containers in general, and to methods and apparatus for providinga protective coating to an area of the metal containers in particular.

2. Background Information

In the manufacture of metal containers such as small tubs of 0.5 litreto several litres capacity, lugs are provided on either side of thecontainer body as anchor points for the carrying handle. These lugs areattached to the bodies preferably by welding or by some other method offixing after the bodies have been resistance spot welded; this, however,means that the protective coating or covering applied to the sheet metalprior to fabrication of the containers is damaged and/or that bare metalis left exposed after the attachment process. These areas of damagedcoating or bare metal then have to be given a protective coating toprevent corrosion by, or contamination of, the product contained. Theinvention can of course be applied to any situation where unprotectedareas of the kind described above are to be covered with a coating forsimilar reasons.

In principle, methods which suggest themselves for covering the areas ofdamaged protective coating or of bare metal are those used to producelarge areas of protective coatings on bare metal. In one such method,can seams are coated by a wet lacquering process in which a lacquer isapplied to the surface to be coated. Disadvantages of this known methodare the long drying times and the solvent vapors given off in the dryingphase, necessitating the increasing use, for environmental reasons, ofspecial extraction systems.

In another known method for covering welded can seams which have beenexposed by the welding process, electrically charged coating powder issprayed between lateral shields on to the weld seam, which is carriedcontinuously past the spraying unit and is therefore “endless”, whileexcess coating powder which accumulates in the shields is continuouslyextracted. The powder which has been sprayed on is then heated inheating lines, which can be up to 20 meters long, and is thereby cured.This known method, which is sometimes also used in the manufacture ofwelded tub bodies (to cover the exposed body seam) is, as has been said,continuous, that is to say endless, and is not suitable for treatingsmall areas. Moreover, it is likely that the intact, already coatedsurface of the containers would be contaminated, which would necessitatesubsequent cleaning, or heating of the entire internal surface of thecontainer in order to bind the pulverulent coating material.

Lastly, there is the option of sticking a foil with protective coatingmaterial over the damaged areas. This known procedure utilizes anadditional substance, namely an adhesive suited to the purpose, and thisshould be avoided if possible, to avoid further contamination andspoiling of the product contained. For containers intended to be filledwith a food product, for example, this would mean that the foodstuffcompatibility of the adhesive would have to be proved and/or approvalobtained from such authorities as the FDA in the USA, which is atime-consuming and expensive process. In any event, the adhesive wouldstill need to be pronounced completely safe for the individual productto be contained, not least in view of the shelf life of up to severalyears expected of metal packaging.

The amount of material absorbed in the process of restoring the coveringlayer is also relevant, as such containers may be manufactured in largenumbers, with the result that the consumption of material (in additionto the capital costs) is a critical factor for the production line.

Accordingly the problem which lies at the basis of the present inventionis to specify a method and an apparatus which are capable of performingthe task with a minimum amount of additional coating material.

DISCLOSURE OF THE INVENTION

This problem is solved by the measures stated in the characterizing partof claim 1. Advantageous configurations of the invention, an apparatusfor carrying out the method and a transport system are indicated infurther claims.

The invention has the following advantages. Because material is appliedonly in the region where bare or damaged areas occur, and there is nolonger any need for surplus powder to be removed, it becomes possible tocover such areas at small cost in terms of coating material.Furthermore, there is no contamination of the container and no givingoff of noxious solvent vapors, as it is possible to work with materialsthat are already recognized and accepted as appropriate, notwithstandingthe fact that the methods used hitherto in the can industry (where lugsmay be unknown) basically cannot be applied to the solution of thepresent problem.

These and other objects, features and advantages of the presentinvention will become apparent in light of the detailed description ofthe invention, and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in detail with reference to drawingsby way of example, in which

FIG. 1 is a perspective view of a lug for welding on to the body of acontainer.

FIG. 2 shows the lug after welding, in a section perpendicular to thebody and also in an end view.

FIG. 3 shows an apparatus according to the invention for covering areasof damaged protective coating on a container.

FIG. 4 is a perspective view of a batching unit used in the apparatusaccording to FIG. 3.

FIG. 5 represents schematically individual phases of a transport systemaccording to the invention.

FIG. 6 is a view from above of one embodiment of the transport systemaccording to FIG. 5, with two rotary manipulators.

FIG. 7 shows a further embodiment of the apparatus according to theinvention for covering areas of damaged protective coating with foil.

FIG. 8 shows different variants of a foil heating unit required in theapparatus according to FIG. 7.

FIG. 9 shows a heating device for heating containers during severalworking steps.

FIG. 10 shows various blanks cut from foil tapes.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a lug 20 which essentially consists of a cylindrical bodywhich has a cover with a hole 21 at one end and a foot 22 extending awayfrom the longitudinal axis of the body at the other end. Weld points,formed e.g. by the spot welding process, are indicated at 23.

FIG. 2A shows the body 24 of a container to which a lug 20 according toFIG. 1 has been attached. The welding process has left areas of damagedprotective coating, indicated at 25, on the inside of the container.These damaged areas 25 correspond to the weld points on the foot 22 ofthe lug 20, and preferably lie in a circle, spaced apart at regularintervals, as shown in FIG. 2B. The problem of the invention is torepair the areas of damaged protective coating so that corrosion of thetub wall, and contamination of the product contained, cannot occur.

Two lugs 20 are provided on each container, and are located oppositeeach other on the outside of the container in the region of thecontainer's upper rim. A carrying handle can be joined in a known mannerto the lugs 20, and thus to the container, by the hole 21. The inventionis of course not limited to the attachment of lugs of this type, and canbe adopted in any situation where a connection has to be made with otherparts, such as tear-off tabs or similar, leaving areas needing to becovered with a protective layer.

FIG. 3 shows one embodiment of apparatus according to the invention forcoating areas of damaged protective coating located on the inside of acontainer 1 which has been provided with lugs 2. In one way of carryingout the invention, the damaged areas are coated by stamping pulverulentcoating material on to the zone susceptible to damage. Pulverulentcoating material is applied by means of a carrier unit 12, preferably aso-called “stamp pad”, which is pressed on to the affected area by meansof a pusher unit 11, causing coating material to be transferred on tothe body of the container 1. Transfer of coating material is assisted ifthe temperature of the container 1, and/or of the region to which thecoating powder is to be applied, is higher than that of the carrier unit12. A heating element 4, which will be described presently, is providedfor this purpose.

After every stamping of coating powder on to the zones subject todamage, the carrier unit 12 has to be recharged with powder. This isdone by means of a rotatably mounted transfer unit 9 which is driven byan angular gear 10 and which preferably has a number of carrier units 12with corresponding pusher units 11 arranged on it. Then, one carrierunit 12 can be picking up coating material while another carrier unit 12is stamping coating material on to the container 1. Yet another carrierunit 12 can be preheated during the same time interval by means of theabove-mentioned heating element 4 in order that, in the ensuing step, itwill be able to pick up coating material which has been prepared on aturntable 3 in a manner which will be described presently, the carrierunit 12 again being actuated by means of the corresponding pusher unit11 to effect such pick-up of material.

As can be seen from FIG. 3, with optimum handling it is possible for thedamaged areas 25 of both lugs 2 welded to the same container 1 to beprovided with coating material. To accomplish this, an additionaltransfer unit 9 of similar construction to the one which has beendescribed, and preferably driven by the same angular gear 10, isprovided. This means that perfectly synchronized coating of the damagedareas at the two lugs 2 is assured, or in other words that the twosymmetrically arranged transfer units 9 work in unison on either side ofthe container 1. Each transfer unit is rotatably mounted and holds fourcarrier units 12 i.e. stamps made of silicone. The carrier units 12 aredisplaced axially by the corresponding pusher unit 11 at every workingstep. In a first step, the carrier unit 12 is pressed on to the heatingelement 4 and preheated so that in the next step it will be able to pickup the prepared coating powder from the turntable 3 as a result of lightadhesion due to heating. In the next step, the carrier unit 12 with thepowder adhering to it is lightly vacuumed to remove any loose powderparticles. This results in greater cleanliness in the container 1. Inthe final step, the carrier unit 12 with the coating powder adhering toit is stamped on to the damaged areas.

To avoid having to move the angular gear 10 and the two transfer units 9up and down, the containers 1 to be coated can be raised by means of anelevating platform 6 to enable the carrier units 12 to stamp coatingpowder on to the damaged areas.

As has already been mentioned, the pulverulent coating material to bestamped on to the damaged areas is removed from the rotatably mountedturntable 3 by the carrier unit 12 concerned. This turntable 3 formspart of a batching unit 31 which also has other components and whichwill now be further described with reference to FIG. 4.

FIG. 4 shows the batching unit 31 in a perspective view. In addition tothe preferably horizontal turntable 3, which has recesses 14 that areabout to be explained and which is preferably rotatable about a verticalaxis 17 and capable of being driven in such rotation by a drive unit 13(FIG. 3), a bin 8 for pulverulent coating material and a cleaning unit16 are provided.

The recesses 14 are filled with coating powder, which runs out from thebottom of the bin 8, up to the level of the top of the turntable 3. Forthis purpose a wiper 18, for example in the form of a strip, is providedbehind the bin 8, viewed in the direction of rotation of the turntable3. In FIG. 4, the reference numeral 15 denotes the transfer position inwhich a carrier unit 12 (FIG. 3) picks up as nearly as possible all thecoating material contained in the recess 14.

Transfer is assisted by heating the carrier unit 12 concerned, or thesurface thereof, by means of the heating element 4 before pick-up takesplace.

After the coating powder is picked up, the turntable 3 goes on turning.When it reaches the cleaning unit 16, at the entry to which a brush 16ais provided, any coating material remaining in the recess 14 is removed.

The configuration of the recesses 14, and hence of the coating patchesactually applied, is such that consumption of coating material can bekept to a minimum and yet is sufficient to ensure that the damagedareas—together with a certain margin—are reliably covered. Moreover, thethickness of the coating applied is set by the depth of the recesses 14.

In keeping with the arrangement of weld points assumed here and in viewof the criteria mentioned above, the chosen form for the recesses 14 isthat of a ring.

The method of handling the containers 1 is shown schematically in FIG.5, in which individual process steps, each corresponding to one segmentof cycle time, are numbered 52 to 58. The same steps and numbers alsoappear in FIG. 6.

Referring to FIG. 5, a container 1, which has already been provided witha bottom, lugs 2, and a handle, is transferred to the coating unit 7,that is to say it is initially placed in position 52. Here the lugs 2are aligned to ensure that the coating m material will be stamped in theright place. By a pendulum step process which will be describedpresently, the containers 1 are individually transported to the nextposition 53, 56 in order that the target zones can be heated with aheating unit 30, designed as an induction heater, hot air blower, orinfra-red radiator. For a more homogeneous contact with the powderadhering to the transfer unit 12, the container 1 is preferably heatedfrom the inside. In one embodiment of the invention, the containers 1are lifted vertically by means of an elevating platform 6, to avoidhaving to move the heating units 30. Hot air or infrared radiation canbe brought to bear from both sides, and can be used simultaneously ifdesired. The container 1—if need be after pausing in a waiting positionW—is then transferred to position 54, where coating material in powderform is applied, preferably in the manner described with reference toFIGS. 3 and 4. Here again the container 1 is raised, to avoid having tomove the batching unit 31 and transfer units 9 together with theirangular gear 10 (FIG. 3). Finally, in position 55, 57, heating againtakes place: by means of heating units 30, the temperature of at leastthe zones subject to damage is raised, preferably to the melting pointof tin. Depending on the melting point of the protective coatingmaterial employed, the requisite temperatures will lie e.g. between 150and 240° Celsius.

FIG. 6 shows a transport system according to the invention in which thepositions 52 to 58 which have been described with reference to FIG. 5are realized in an arrangement that is compact and allows for rigidlyimposed transport cycle times. The application of coating takes place ina production line for the containers concerned which may extend from thecutting-up of sheet-metal blanks to form the containers to the fillingand closure of the containers, so that the transport cycle ispreordained. With the aid of a rotary manipulator 60 the containers 1can be preheated in tandem, one being heated while the other is beingtransported and vice versa.

To heat a container, the container is transferred, by means of suctioncups 62 or the like forming part of the rotary manipulator 60, fromposition 52 to position 53, where it is parked. In the next step of thecycle, the next container arriving in position 52 is picked up andtransferred to position 56. During this transfer phase, the containerparked in position 53 stays where it is. Not until a container has beenparked in position 56 is the container in position 53 picked up again,and transferred by rotation of the manipulator 60 to position 54, wherefor example the stamping-on of coating powder as described withreference to FIGS. 3 and 4 takes place. The second rotary manipulator 61is used in a similar way.

In this way, the heating phase is extended without affecting thefundamental cycle time. If baking is necessary following application ofthe coating powder, a second rotary manipulator 61, connected in series,will be required, again giving the heating unit 30 (FIG. 5) an extendeddwell time.

The method according to the invention and the transport system accordingto the invention are particularly suited for mechanized and continuousoperation in a production line, as has already been stated. Over 80cycles per minute can be achieved. Consumption costs can be kept to aminimum by the precise nature of the batching. With the method accordingto the invention, contamination of the container with loose powder doesnot occur, as any loose powder will stay stuck to the carrier units.

In another embodiment of the invention, instead of using stamping padsas carrier units these are formed as a solid bar of protective coatingmaterial. Shortly before being stamped on to the damaged areas, the barend is melted and/or the target zones are preheated to a temperatureabove the melting point of the coating material. This involves onlyminor modifications of the apparatus according to the invention. Forinstance the batching unit in the form described is no longer required.But the essence of the inventive idea still remains.

In one embodiment of the apparatus according to the invention, a foiltape which is cut up into blanks is used instead of powder. These blanksare then picked up by the transfer unit and applied to the inner wall ofthe container in the same way as a prepared ring of powder. Theapparatus can remain essentially unchanged, the only difference beingthat the bin 8 will then be dispensing foil blanks instead of powder onto the turntable 3. An expert will be capable of making the necessarymodifications without needing further instruction.

A preferred embodiment of an apparatus for applying blanks will bedescribed with reference to FIGS. 7 to 10.

FIG. 7 shows the preferred embodiment of the invention in a partlycutaway view perpendicularly to the transport direction of thecontainers 1. The containers 1 are transported in a series of steps;before the application of foil (and if a heating device—which will beexplained later (FIG. 9)—is used, before reaching the heating device),the containers 1 are aligned so that the point of application is inregister with the position of the lugs 2. Preferably, the containers 1are aligned so that the lugs 2 are located laterally when viewed in thetransport direction.

Foil 100 is supplied from a reel 107 located in a hot box 112 under thetransport system for the containers 1. In the case of the apparatusillustrated in FIG. 7, the foil tape 100 is double-wound on the reel107. This makes it possible by means of suitable deflection pulleys 102to 104 to convey the foil 100 to the transfer unit in a simple manner,as follows: the foil tape is fed by means of a tape feed unit and tapeholder 109 which are operated alternately, and the foil 100 is cut intothe desired shapes by means of a punch 108 and transferred to thetransfer unit 9 fitted with carrier units 12. Here the carrier units 12preferably consist of so-called “stamp pads” which pick up the foilblanks by suction. These stamp pads have holes at suitable points whichcommunicate with a chamber connected in turn to a low-power vacuum pump.

In FIG. 7 the transfer unit 9 has been drawn in two positions. In theupper position, the carrier unit 12 is charged with a blank of foilmaterial. A container 1 with areas of damaged protective coating in theregion of the lugs 2 has been prepared and placed in position underneaththe transfer unit 9. The transfer unit 9 is then moved to the second,i.e. lower, position by means of a pneumatic or hydraulic cylinder 111.A further, horizontally mounted cylinder presses the carrier units 12charged with blanks radially outwards at the same level as the lugs 2,so that the blanks are applied to the areas of damaged protectivecoating. Prior to the application of the blanks, the container 1 isheated, in a manner which will be described presently, to a temperatureaffording ideal conditions for joining the foil material to the interiorof the container.

Polyamide-12 (also known under the trade name. NYLON), polyamide-6 andpolyester have all proved suitable as foil material, especiallypolyamide-12. In the case of the last mentioned product, the containers1 and/or their interiors in the region of the lugs 2 are preferablyheated to a temperature of approx. 160° Celsius. This ensures perfectbonding of the foil material to the inner wall of the container.

At the same time, the hot box 112 containing the reel 107 of foil tapeis heated to a temperature of approx. 80° Celsius. This prepares thefoil material for the application process. Any water droplets which mayhave been deposited on the tape are evaporated by this warming processbefore the foil is applied. This will effectively prevent flaking.

In a further embodiment of the apparatus according to the invention,shown in FIG. 8A, a skid 113 is substituted for the hot box 112. Thefoil tape is guided along this skid 113, which is heated toapproximately 100° Celsius. This again prevents water droplets frombeing deposited on the foil tape, and evaporates any water dropletswhich may be present.

FIG. 8B shows an alternative embodiment to the skid 113 shown in FIG.8A. The foil tape is guided through a hot-air tunnel 114 which performsthe functions stated above.

FIG. 9 shows an arrangement for three-stage heating of the areas ofdamaged coating on the interior of the containers 1, which are advancedin steps in the direction of the arrow 120 by means of a transportsystem (not shown in FIG. 9). During the stages when the containers areat rest, hot air supply lines 124, 125, 126 are positioned in the opentopped containers over the damaged areas. In synchronization with theadvance of the containers 1 in the direction 120, a drive unit 121 istriggered so that the supply lines 124, 125, 126 do not come intocontact with the containers 1. The drive unit 121 is coupled with theheat supply lines 124, 125, 126 by drive belts 122 and swiveling axes127, 128, 129. The heat supply lines 124, 125, 126 are supplied with hotair via a heating air duct 123, in which they are pivotally mounted.

With the proposed heating device, there is no need to vary the transportcycle for the containers 1 even if the heating operation has to beperformed in a number of cycles. Also, the amount of movement of theheating assemblies is minimal.

FIG. 10 shows some foil tapes 100 and blanks 150, 151, 152 takentherefrom. For example, FIG. 10A shows rectangular blanks 150 which canbe made without leaving any waste.

In FIG. 10B, round blanks 151 are produced by means of a punch 108 (FIG.7A). A strip of waste 155 is left over.

Lastly, FIG. 1 OC shows the preferred type of blank. By means of thepunch 108 (FIG. 7A), blanks 152 are produced that are circular exceptfor two straight segments. The intermediate pieces 156 that are leftover as waste are extracted by means of an extraction device 110.

The invention can be used to advantage in other applications besides thecovering of areas of damaged protective coating on containers. Theinvention is highly suitable for covering areas on components of anydescription.

Although this invention has been shown and described with respect to thedetailed embodiments thereof, it will be understood by those skilled inthe art that various changes in form and detail thereof may be madewithout departing from the spirit and the scope of the invention.

What is claimed is:
 1. A method for manufacturing a metal container,comprising the steps of: welding one or more lugs to the metal containerat predetermined positions, wherein after the welding process an area ofdamaged protective coating is disposed proximate each of thepredetermined positions; stamping a protective coating material onto thearea of damaged protective coating; and heating the area to which theprotective coating material has been applied to stabilize the protectivecoating material.
 2. The method of claim 1 wherein said protectivecoating material is in pulverant form.
 3. The method of claim 2, whereinthe stamping of the protective coating material is performed using acarrier unit, wherein the carrier unit transports the protective coatingmaterial from a source to the container.
 4. The method of claim 3,further comprising the step of heating the container to a firsttemperature prior to stamping the protective coating material, whereinthe carrier unit is at a second temperature, and the first temperatureis higher than the second temperature.
 5. The method of claim 4, whereinthe carrier unit is heated to the second temperature, which is higherthan ambient temperature, prior to transporting the protective coatingmaterial.
 6. The method of claim 5, further comprising the step ofvacuuming the carrier unit after the carrier unit transports theprotective coating material away from the source, but before the carrierunit transports the protective coating material to the container.
 7. Themethod of claim 1, wherein the protective coating material is a solidbar that has a stamping end that is heated to approximately the meltingpoint of the protective coating material prior to stamping, whereinmaterial from the heated solid bar is transferred to the containerduring the stamping.
 8. The method of claim 1, wherein the protectivecoating material is a foil tape.
 9. The method of claim 8, wherein thestamping of the protective coating material is performed using a carrierunit, and wherein the carrier unit transports blanks of the foil tapefrom a source to the container.
 10. The method of claim 9, wherein thefoil tape is preheated to a temperature higher than ambient prior tostamping.
 11. An apparatus for coating an area of damaged protectivecoating on a container, comprising a source of protective coatingmaterial; at least one carrier unit; at least one pusher, wherein the atleast one pusher selectively actuates the carrier unit into contact withthe source of protective coating material, and selectively actuates thecarrier unit into contact with the area of damaged protective coating onthe container, thereby stamping protective coating material attached tothe at least one carrier unit onto the area of damaged protectivecoating on the container; and a first heater for heating the area of thecan to which the protective coating material has been deposited tostabilize the protective coating material.
 12. The apparatus of claim11, further comprising a second heater for heating the at least onecarrier unit.
 13. The apparatus of claim 12, wherein the first heater iscapable of heating the container to a first temperature prior tostamping the protective coating material, and wherein the second heateris capable of heating the carrier unit to a second temperature, and thefirst temperature is higher than the second temperature.
 14. Theapparatus of claim 12, further comprising a vacuum for vacuuming thecarrier unit after the carrier unit is selectively actuated into contactwith the source of protective coating material, and before the carrierunit is selectively actuated into contact with the area of damagedprotective coating on the can.
 15. The apparatus of claim 11, whereinthe source of protective coating material is a foil tape, and the pusherselectively actuates the carrier unit into contact with the foil tape.16. The apparatus of claim 15, further comprising a third heater forheating the foil tape to a temperature higher than ambient prior tostamping.
 17. The apparatus of claim 11, further comprising: a rotatabletransfer unit for mounting a plurality of carrier units and a likenumber of pushers; and a drive for selectively rotating the transferunit; wherein the drive selectively rotates each carrier unit between afirst position proximate the source of protective coating material and asecond position proximate the container; and wherein each pusherselectively actuates the carrier unit into contact with the source ofprotective coating material, and selectively actuates the carrier unitinto contact with the area of damaged protective coating on thecontainer.
 18. The apparatus of claim 17, further comprising a secondheater for heating one the plurality of carrier units, wherein the driveselectively rotates each carrier unit to a third position proximate thesecond heater.
 19. The apparatus of claim 17, further comprising atleast one selectively moveable platform for supporting the container,wherein the container is disposed on then platform in a first positionand the platform can be selectively moved to a second position so thatthe area of damaged protective coating on the container is proximate therotatable transfer unit.
 20. The apparatus of claim 17, wherein thesource of protective coating material comprises: a rotatable turntable;a bin; and a cleaning unit; wherein the bin and the cleaning unit aredisposed on a side of the turntable; and wherein the bin and cleaningunit are positioned such that protective coating material selectivelyreleased from bin is deposited on the rotatable turnable, and therotatable turntable rotates to expose the deposited protective coatingmaterial to one of the carrier units, and subsequently rotates to allowthe cleaning unit to remove whatever protective coating material is leftafter the respective carrier unit is selectively actuated into theprotective coating material deposited on the turntable.
 21. Theapparatus of claim 20, wherein the turntable comprises a plurality ofrecesses positioned to receive protective coating material from the bin.22. The apparatus of claim 21, wherein the bin includes a wiper disposedin contact with the turntable.
 23. The apparatus of claim 21, whereinthe cleaning unit includes a brush in contact with the turntable.
 24. Anapparatus for coating an area of damaged protective coating on acontainer, comprising a solid rod of protective coating material; afirst heater for heating a stamping end of the solid rod toapproximately the melting point of the protective coating material; apusher for actuating the solid rod into contact with the area of damagedprotective coating on the container, thereby enabling the deposition ofprotective coating material onto the container; and a first heater forheating the area of the can to which the protective coating material hasbeen depositied to stabilize the protective coating material.